Rock revetment project in final permitting stages

More protection needed for wastewater treatment facility located in tsunami zone

March 23, 2014

Maui County is in the final stages of permitting for an estimated $4.5 million rock revetment extension to protect the Wailuku-Kahului Wastewater Reclamation Facility from erosion, county officials said.

The county filed for a shoreline certification with the state Department of Land and Natural Resources earlier this month, according to a notice released March 8 from the state Office of Environmental Quality Control.

Department of Environmental Management Director Kyle Ginoza said his department expects to have the remaining permits secured within the next 90 days and has already contracted Goodfellow Bros. Inc. to construct the project.

Article Photos

Maui County plans to build a $4.5 million rock revetment extension along this Kahului shoreline to protect the Wailuku-Kahului Wastewater Treatment Facility (at left) from erosion and tsunami inundation. The project is in its final permitting stages, county officials report. Goodfellow Bros. Inc. has been contracted to build the seawall extension.

The Maui News / BRIAN PERRY photo

Construction is expected to start July 1 and take about a year to complete, Ginoza said.

The project calls for extending the existing 450-foot seawall built in 1979 by adding about 1,100 feet of new rock revetment to the west of the existing seawall, according to the final environmental impact statement published last April. The document cites a Hawaii Shoreline Study finding that, from 2007 to 2011, erosion at the site averaged 3.7 feet per year, with a maximum erosion rate of 6.7 feet. The plant's eight injection wells could be threatened in two years and a sludge holding tank within three years without protection measures, officials said.

The crest of the new revetment will be 10 to 13 feet above sea level and the toe of the wall will be 3 feet below sea level. The top of the existing revetment will be raised to match the height of the new rock wall. A layer of geotextile filter fabric will be at the base of the revetment, then a layer of bedding stones and two layers of armor stone, according to a project description.

The project has been modified from the original proposal "to minimize impact to both the environment and ocean users," Ginoza said in an email.

While the original proposal called for a 1,200-foot "exposed" rock mound revetment along the beach, the current project aligns the revetment more inland to "minimize impacts to biological resources, recreational beach area and adjacent beaches," according to the final environmental impact statement. Additionally, two 125-foot-long sections at each end of the revetment would curve inland, preventing flanking erosion. The overall length of the revetment will be 1,350 feet, about 900 of which will be mauka of the shoreline.

Lateral beach access will be maintained at all times, Ginoza said.

But some residents voiced concerns in earlier community meetings about the project causing beach erosion, negative impacts for recreational ocean users and greater damage if there were a severe tsunami.

"The proposed 13-foot-high seawall will not work if we have a tidal wave like the one we had in 1946," Maui architect Tom Cannon said Tuesday. The 1946 tidal waves that hit Maui and other Hawaiian islands reached upward of 28 feet.

Cannon said that, in the event of another tsunami of a similar magnitude, the proposed seawall would not only fail to protect the facility, but it would add debris that would be pushed inland by rushing waves.

"If the returning debris includes 2-ton stones dislodged from the proposed seawall . . . these objects will become battering rams destroying any buildings or sewage effluent tanks in their path," Cannon said in a written statement he submitted to the county.

He added it "was a mistake to put it (the wastewater treatment plant) there in the first place," and he suggested that the facility be moved inland, out of a tsunami-evacuation zone.

For years, county officials considered relocating the facility, and they commissioned a study in 2005 to determine relocation costs. At the time, the estimated cost of a new facility ranged from $350 million to $475 million.

The Maui County Council considered a few options in 2006, but council members were told that it was unlikely the county would receive any financial help from the state or federal governments, The Maui News reported then.

Because of the steep "price factor," county officials opted to protect the existing facility by mitigating tsunami impact risk and armoring the shoreline fronting the facility. The seawall revetment project, once completed, should be able to withstand a tsunami with waves of 20 feet and higher, officials said.

At least one contractor has offered to complete the relocation project for significantly less - about $150 million - but county officials said that without state or federal help, even that is a heavy load to pass on to county taxpayers.

Sewage plant operators also must consider other effects of moving the sewage treatment facility mauka, such as foul-smelling odors and safety hazards in the event of a leak.

"Water flows to lower elevation, and the shoreline is usually the lowest," county Department of Environmental Management Deputy Director Michael Miyamoto said. "So do you want to pump raw sewage inland or reclaimed water inland?"

The plant, built in 1973, treats more than 5 million gallons per day. It has a daily capacity of 7.9 million gallons. It serves developed areas of Waiehu, Wailuku, Kahului, Spreckelsville and Paia.